Purification means

ABSTRACT

Polymers derived from 4-acyloxystyrene are purified by fractionalization plus heating and cooling of the polymers in alcoholic solvents.

RELATED APPLICATION

[0001] The present application is a continuation-in-part of and isrelated by common assignee to Ser. No. 09/604,140 filed Jun. 27, 2000.

BACKGROUND OF THE INVENTION

[0002] Copolymers and terpolymers, when isolated from reaction solutionare a mixture of compounds of varying composition and molecular weight.Typically they contain small quantities of starting material andby-products which are undesirable in the final polymer. The polymermixture is precipitated from the solvent or solvent mixture by addingthe mixture to a second solvent, as for example water, hexane, heptane,octane, petroleum ether, or a mixture thereof. The polymer is then driedunder a nitrogen atmosphere. The subject of this invention pertains to amethod of purifying the polymer.

[0003] Davidson, in U.S. Pat. No. 5,945,251, discloses a method ofpurifying polyhydroxystyrene polymers by adding an amine, a hydrophilicsolvent, a hydrophobic solvent, and water to the polymer; separating theaqueous phase; then removing the hydrophilic solvent and the hydrophobicsolvent to form the purified polymer.

[0004] Zempini, et al. in U.S. Pat. Nos. 5,789,522 and 5,939.511,extracts impurities from a phenolic resin by dissolving the resin in aphotoresist solvent and extracting the water-soluble impuritiestherefrom.

SUMMARY OF THE DISCLOSURE

[0005] The present invention provides a novel process for improving theglass transition temperatures and reducing the polydispersity valuesofpolymer intermediates that have been polymerized by precipitation frommethanol. The polymers that are susceptible to treatment with the methodof this invention are polymers of 4-acyloxystyrene. The 4-acyloxystyrenederived polymers are then transesterified to 4-hydroxyphenyl-containingpolymers useful in paints, resins, thickening agents, and in photoresistcompositions. The present invention process is an improvement over theprior art and is quite efficient. Specifically the invention provides amethod of removing unreacted monomers, low molecular weight polymers,and the like from the crude polymer mixture before thetransesterification step. Many analytical methods can be utilized toquantify the improvement in the purity of polymers. Average molecularweight, nuclear magnetic resonance, chromatography, and glass transitiontemperature are all effective in certain instances with certainmolecules and characteristic side chains.

[0006] As previously described in the prior art, the crude polymer afterpolymerization is separated from the alcohol by filtration,centrifugation, decantation, or the like. According to the method ofthis invention, the polymer is subject to fractionalization whereby itis suspended in methanol and the solid is separated from the methanol.This procedure is repeated as long as necessary to remove by-productsand low molecular weight materials that are more soluble in the methanolthan the desired polymer. In this manner, the undesirable monomericimpurities and oligomers are soluble in the solvent (such as methonal)depending upon temperature and thus are removed during eachfractionation step.

DETAILED DESCRIPTION OF THE INVENTION

[0007] This invention provides a process for the improvement in thecomposition of polymers derived from the monomer I,

[0008] wherein R is either —OC(O)R⁵ or —OR⁵; as a homopolymer and/ortypically with one or more of the following monomers:

[0009] an acrylate monomer having the formula II,

[0010]  and/or with one or more ethylenically unsaturatedcopolymerizable monomers (EUCM) selected from the group consisting ofstyrene, 4-methylstyrene, styrene alkoxide wherein the alkyl portion isC₁-C₅ straight or branch chain, tert.-butylstyrene, cyclohexyl acrylate,tert.-butyl acrylate, tert.-butyl methacrylate, maleic anhydride,dialkyl maleate, dialkyl fumarate and vinyl chloride. wherein:

[0011] i) R¹ and R² are the same or different and independently selectedfrom the group consisting of:

[0012] hydrogen;

[0013] fluorine, chlorine or bromine;

[0014] alkyl or fluoroalkyl group having the formula C_(n)H_(x)F_(y)where n is an integer from 1 to 4, x and y are integers from 0 to 2n+1,and the sum of x and y is 2n+1; and

[0015] phenyl or tolyl;

[0016] ii) R³ is selected from the group consisting of:

[0017] hydrogen; and

[0018] methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl ortert.-butyl;

[0019] iii) R⁴ is methyl, ethyl, n-propyl, iso-propyl or tert.-butyl;and

[0020] iv) R⁵ is C₁-C₄ alkyl,

[0021] typically manufactured by subjecting a monomer of formula I,

[0022] or a monomer of the formula I and/or monomer II, and/or one ormore of said copolymerizable monomers (EUCM) to suitable polymerizationconditions in an alcoholic solvent and in the presence of a free radicalinitiator at suitable temperature for a sufficient period of time toproduce a crude polymer of corresponding composition. After purificationby the method of this invention, the purified polymer is transesterifiedto a polymer containing the monomer of formula III:

[0023] by (1) subjecting said polymer to transesterification conditionsin said alcoholic solvent in the presence of catalytic amounts of a basecatalyst at suitable temperature such that the transesterifiedby-product ester formed is continuously removed from the reactionmixture to form the homopolymer of I or the copolymer of I, and/or II,and/or said copolymerizable monomer, (EUCM) or

[0024] (2) subjecting the polymer to acidic hydrolysis with a strongacid. The polymer is then optionally passed through an ion-exchange bedto remove said base or acid catalyst;

[0025] The polymerization, purification, and/or transesterificationsteps are carried out on an anhydrous basis (i.e. <about 5,000 ppmwater). The alcoholic solvent for the polymerization is an alcoholhaving 1 to 4 carbon atoms and is selected from the group consisting ofmethanol, ethanol, propanol, isopropanol, t-butanol, and combinationsthereof. The amount of solvent used is not critical and can be anyamount which accomplishes the desired end result.

[0026] The free radical initiator for the polymerization may be anyinitiator that achieves the desired end result. The initiator may beselected from the group consisting of2,2′-azobis(2,4-dimethylpentanenitrile),2,2′-azobis(2-methylpropanenitrile), 2,2′-azobis(2-methylbutanenitrile),1,1′-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate,t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide,decanoyl peroxide, succinic acid peroxide, di(n-propyl)peroxydicarbonate, di(sec-butyl) peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, t-butylperoxyneodecanoate,2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane,t-amylperoxyneodecanoate, dimethyl 2,2′-azobisisobutyrate, andcombinations thereof.

[0027] The initiator is typically selected from the group consisting of2,2′-azobis(2,4-dimethylpentanenitrile),2,2′-azobis(2-methylpropanenitrile), 2,2′-azobis(2-methylbutanenitrile),1,1′-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate,t-butyl peroxypivalate, t-amyl peroxypivalate, and combinations thereof.

[0028] The polymerization conditions are not critical and can be anytemperature and pressure that will produce the desired end result. Ingeneral, the temperatures are from about 30° C. to about 100° C.,preferably from about 40° C. to about 100° C., and most preferably fromabout 45° C. to about 90° C. The pressure may be atmospheric,sub-atmospheric or super-atmospheric. The polymerization time is notcritical, but generally will take place over a period of at least oneminute in order to produce a polymer of corresponding composition.

[0029] After the polymerization step and prior to thetransesterification step, the crude polymer is subjected to apurification procedure wherein the same type carboxylic alcoholicsolvent (first solvent) is used to purify the crude polymer via amulti-step fractionation process. Additional first solvent is added tothe crude polymer mixture, and the resultant slurry is stirredvigorously and/or heated to boiling (about 66° C.) for several minutes,and then chilled to as low as 25° C. and allowed to stand. This permitsthe slurry to produce a phase separation, and then the liquid is removedby centrifugation, filtration, decantation or by similar means. Theprocess is repeated at least one more time until no further purificationis identified, as for example, until a small sample of the decantedsolvent, upon evaporation to dryness shows substantially no residue.This fractionation process is generally carried out 2 to 10 times, i.e.heating, cooling, separating, and the solvent replacement.

[0030] One of the important measures of the degree of impurity of thecrude polymer produced from the polymerization of the monomers is thepolydispersity value. In general, it is desirable to have a low value,for example, less than about 3; the lower value is indicative that thepolymerization reaction was more uniform in chain length. The uniquenessof this purification step is that the desired polymer formed is to somedegree not soluble in the solvent and that the undesired, low molecularweight average polymers and undesired monomers are soluble in thesolvent. Thus the novel purification/fractionalization step, providesthe removal of these undesirable materials. In general thepolydispersity of the crude polymer is measured before, during and afterthis purification/fractionalization step, with the objective of reducingthis value by at least about 10% of what the value of the original crudepolymer was before the purification treatment. Preferably it isdesirable to yield a product whose polydispersity is below about 2.0. Itis to be understood that polydispersity means the ratio of weightaverage molecular weight (Mw) over the number average molecular weight(Mn) as determined by Gel Permeation Chromatography (GPC).

[0031] In the transesterification step, the purified polymer from thepolymerization step is subjected to said transesterification conditionsin an alcoholic solvent in the presence of catalytic amounts of a basecatalyst. The base catalyst is such that it will not substantially reactwith said alkyl acrylate monomer II, or with said co-polymerizablemonomers (EUCM). The base catalyst is either an alkalic metal hydroxideor an alkalic metal alkoxide. The base catalyst is selected from thegroup consisting of lithium hydroxide, lithium methoxide, lithiumethoxide, lithium isopropoxide, sodium hydroxide, sodium methoxide,sodium ethoxide, sodium isopropoxide, potassium hydroxide, potassiummethoxide, potassium ethoxide, potassium isopropoxide, cesium hydroxide,cesium methoxide, cesium ethoxide, cesium isopropoxide, and combinationsthereof.

[0032] If a hydrolysis is utilized to effect removal of the phenolblocking group, the acid should be a member of the strong acids, as forexample hydrochloric acid, hydrobromic acid, sulfuric acid, or the like.

[0033] Thus and according to the method of this invention, afterpolymerization of the acyloxy-derived polymer, and prior to thetransesterification the crude polymer is subjected to this novelfractionation process which provides a substantially purified polymerwhich then can be further treated.

[0034] This invention is further illustrated by the following examplesthat are provided for illustration purposes and in no way limits thescope of the present invention.

EXAMPLES (GENERAL)

[0035] In the Examples that follow, the following abbreviations areused:

[0036] ASM—p-Acetoxystyrene monomer

[0037] t-BPP—tert-butyl peroxypivalate

[0038] THF—Tetrahydrofuran

[0039] GPC—Gel permeation chromatography

[0040] GC—Gas chromatography

[0041] FTIR—Fourier transform infrared spectroscopy

[0042] NMR—Nuclear magnetic resonance spectroscopy, usually of eitherproton, ¹H;

[0043] and/or carbon 13, ¹³C nuclei.

[0044] DSC—Differential scanning calorimetry

[0045] UV-Vis—Ultraviolet-Visible Spectroscopy

[0046] General Analytical Techniques Used for the Characterization: Avariety of analytical techniques were used to characterize the co- andterpolymers of the present invention that included the following:

[0047] NMR: ¹H and ¹³C NMR spectra were recorded on a Bruker 400 MHzspectrometer with 5 mm probes at 400 and 100 MHz, respectively.

[0048] GPC: GPC was performed on a Waters gel permeation chromatographequipped with refractive index detection.

[0049] GC: GC analysis was performed on a Hewlett Packard Model 5890series II gas chromatograph equipped with a DB-1 column.

[0050] FTIR: FTIR was recorded on a Mattson Genesis Series FTIR.

[0051] DSC: A Perkin Elmer 7700 DSC was used to determine the T_(g)(glass transition temperature) of the co- and terpolymers of thisinvention. The heating rate was maintained at 10° C./minute, generally,over a temperature range of 50° C. to 400° C. The flow rate of nitrogenor air is maintained at 20 mL/min.

[0052] UV-Vis of samples were taken using a Hewlett Packard Vectra486/33VL UV-Vis spectrophotometer.

Example 1 Poly(4-hydroxystyrene) in propyleneglycolmonomethyl etheracetate

[0053] To a four neck 12 liter flask, fitted with a mechanical stirrer,condenser, nitrogen inlet and thermowell, 4-acetoxystyrene (2752.3 g,16.97 moles), and methanol (3075.0 g) were added. The flask was purgedwith nitrogen and then heated to reflux (66° C.) over a period of onehour. Then, 2,2′-azobis(2,4-dimethylvaleronitrile) (146.0 g, 0.59 moles)was added to the hot reactor as a slurry in methanol (250 g). Thereactor was heated at reflux for 2 hours and then an additional chargeof 2,2′-azobis(2,4-dimethylvaleronitrile) (24.3 g, 0.1 moles) was done.The reactor was heated for an additional 6 hours and then was cooled toroom temperature.

[0054] The solids were extract by successive replacements of the solventas follows. The reactor was heated to 60° C. with stirring. The heat wasremoved and the reactor was allowed to cool without stirring to 44.3° C.The top layer (899 g) of solvent was removed by suction and was replacedwith methanol (1495 g). The reactor was again heated to 60° C. andcooled to 41.9° C. without stirring. The top layer (1700 g) was againremoved by suction and was replaced with methanol (1705 g). The reactorwas again heated to 60° C. and cooled to 46.2° C. without stirring. Thetop layer (1633 g) was again removed by suction and was replaced withmethanol (1765 g). The reactor was again heated to 60° C. and cooled to45.0° C. without stirring. The top layer (1905 g) was again removed bysuction and was replaced with methanol (1955 g). The reactor was againheated to 60° C. and cooled to 46.0° C. without stirring. The top layer(2145 g) was again removed by suction and was replaced with methanol(2215 g). The reactor was again heated to 60° C. and cooled to 46.0° C.without stirring. The top layer (2241 g) was again removed by suctionand was replaced with methanol (1700 g). All of the solids during eachextraction were analyzed for molecular weight by GPC, table I. Thereactor was then cooled to room temperature.

[0055] The purified poly(4-acetoxystyrene) was converted topoly(4-hydroxystyrene) as follows. The reactor was fitted with a DeanStark trap and condenser. A solution of 25.0 weight percent of Sodiummethoxide in methanol (64.24 g, 0.30 moles) was added to the reactor.The reactor was then heated to reflux (64° C.). The overhead distillatewas removed and replaced with methanol with equal weight. The reactorwas heated at reflux for 7.5 hours. The reactor was then cooled to roomtemperature. This solution was then passed through a column of AmberlystA15 (2×″16″) at 40 mL/min at room temperature to remove metalcontamination.

[0056] The solvent was exchanged from methanol topropyleneglycolmonomethyl ether acetate (PGMEA) as follows. The solutionwas added to a 4 neck, 12 liter flask fitted with a distillation headand receiver, thermowell, mechanical stirrer, and nitrogen inlet. Thereactor was heated to 25° C. to 48° C. under vacuum (120 torr to 10torr) to remove methanol. To the reactor, a total of 4975 g PGMEA wasadded as the methanol was removed. The amount of solids present wasdetermined by density and the solution was adjusted to 35.0 weightpercent with PGMEA. An overall yield of 1634 g of polymer (81.7%theoretical yield) was obtained.

Example 2 Poly(4-hydroxystyrene) in propyleneglycolmonomethyl etheracetate

[0057] To a four neck 12 liter flask, fitted with a mechanical stirrer,condenser, nitrogen inlet and thermowell, 4-acetoxystyrene (2752.3 g,16.97 moles), and methanol (3081.0 g) were added. The flask was purgedwith nitrogen and then heated to reflux (66° C.) over a period of onehour. Then, 2,2′-azobis(2,4-dimethylvaleronitrile) (146.1 g, 0,59 moles)was added to the hot reactor as a slurry in methanol (250 g). Thereactor was heated at reflux for 2 hours and then an additional chargeof 2,2′-azobis(2,4-dimethylvaleronitrile) (24.4 g, 0.01 moles) was done.The reactor was heated for an additional 6 hours and then was cooled toroom temperature.

[0058] The solids were extracted by successive replacements of thesolvent as follows. The reactor was heated to 60° C. with stirring. Theheat was removed and the reactor was allowed to cool without stirring to45.0° C. The top layer (1129 g) of solvent was removed by suction andwas replaced with methanol (1817 g). The reactor was again heated to 60°C. and cooled to 47.0° C. without stirring. The top layer (1627 g) wasagain removed by suction and was replaced with methanol (1624 g). Thereactor was again heated to 60° C. and cooled to 44.0° C. withoutstirring. The top layer (1668 g) was again removed by suction and wasreplaced with methanol (1613 g). The reactor was again heated to 60° C.and cooled to 47.0° C. without stirring. The top layer (1514 g) wasagain removed by suction and was replaced with methanol (1745 g). Thereactor was again heated to 60° C. and cooled to 45.0° C. withoutstirring. The top layer (1822 g) was again removed by suction and wasreplaced with methanol (2288 g). The reactor was again heated to 60° C.and cooled to 43.0° C. without stirring. The top layer (22471 g) wasagain removed by suction and was replaced with methanol (1607 g). All ofthe solids during each extraction were analyzed for molecular weight byGPC, table 1. The reactor was then cooled to room temperature.

[0059] The purified poly(4-acetoxystyrene) was converted topoly(4-hydroxystyrene) as follows. The reactor was fitted with a DeanStark trap and condenser. A solution of 25.0 weight percent of Sodiummethoxide in methanol (64.24 g, 0.30 moles) was added to the reactor.The reactor was then heated to reflux (64° C.). The overhead distillatewas removed and replaced with methanol with equal weight. The reactorwas heated at reflux for 7.5 hours. The reactor was then cooled to roomtemperature. This solution was then passed through a column of AmberlystA15 (2×″16″) at 40 mL/min at room temperature to remove metalcontamination.

[0060] The solvent was exchanged from methanol topropyleneglycolmonomethyl ether acetate (PGMEA) as follows. The solutionwas added to a 4 neck, 12 liter flask fitted with a distillation headand receiver, thermowell, mechanical stirrer, and nitrogen inlet. Thereactor was heated to 25° C. to 48° C. under vacuum (120 torr to 10torr) to remove methanol. To the reactor, a total of 4000 g PGMEA wasadded as the methanol was removed. The amount of solids present wasdetermined by density and the solution was adjusted to 35.0 weightpercent with PGMEA. An overall yield of 1708 g of polymer (85.4%theoretical yield) was obtained. TABLE 1 Molecular weight analysis ofpoly(4-acetoxystyrene) purification by extraction. Example 1 Example 2Weight average Number average Weight average Number average SampleMolecular Weight Molecular Weight Polydispersity Molecular WeightMolecular Weight Polydispersity Original solid 9,556 5,083 1.88 8,8664,501 1.97 1^(st) extraction 9,845 5,594 1.76 9,830 5,093 1.93 2^(nd)extraction 10,009 5,888 1.70 10,049 5,742 1.75 3^(rd) extraction 10,3716,285 1.65 10,112 5,879 1.72 4^(th) extraction 9,921 6,162 1.61 10,3275,969 1.73 5^(th) extraction 10,362 6,476 1.60 9,394 5,559 1.69

Example 3 Poly (hydroxystyrene-co-ethoxyethoxystyrene)

[0061] To a 3 L 4 neck round bottom flask containing 1.30 kg, 34.5 wt %polyhydroxystyrene solution in PGMEA, camphoresulphonic acid, 400 mg wasadded under nitrogen atmosphere and the mixture was stirred at 23° C.for 2 hours for homogeneity. The solution was then cooled to 5° C. and127 g, ethylvinylether was added drop wise with stirring under nitrogenat the reaction temperature between 5° C. to 10° C. (2 hours). After theaddition, the mixture was stirred for additional 6 hours at 5° C.Amberlyst A-21, 33 g which was pretreated with PGMEA was added to thereaction mixture and stirred for 2 hours at 25° C. The resin was removedby filtration and 1.43 kg, 39.3% poly(hydroxystyrene-co-ethoxyethoxystyrene) copolymer solution was obtained.The characterization of the copolyrner and the ratio determination weredone by NMR. Hydroxystyrene/ethoxyethoxy-styrene ratio was determined tobe 60/40, molecular weight was determined by GPC (polystyrene standard)to be Mw=10,819 with the polydispersity 1.77.

Example 4 Poly (hydroxystyrene-co-t-butoxycarbonyloxystyrene)

[0062] To a 2 L round bottom flaks containing 1.03 kg, 35.1 wtl %polyhydroxystyrene solution in PGMEA, p-dimethlyaminopyridine, 0.72 g in11 g PGMEA was added under nitrogen and the mixture was stirred at 23°C. for one hour. Di-t-butyl dicarbonate, 124.4 g was added to thesolution at 23° C. and stirred under nitrogen for 6 hours at 23° C.Vacuum was applied to the solution at 20 mmHg with stirring for 1 hourat 23° C. for removal of carbon dioxide formed as a by-product in thesolution. Dowex Mac-3, 30 g which was pretreated with PGMEA was added tothe reaction mixture and stirred for 2 hours at 23° C. The resin wasremoved by filtration and 1.14 kg, 36.6 wt % poly(hydroxystyrene-co-t-butoxycarbonyloxystyrene) copolymer solution wasobtained. The characterization of the copolymer and the ratiodetermination were done by NMR.Hydroxystyrene/t-butoxycarbonyloxystyrene ratio was determined to be82/18, molecular weight was determined by GPC to be Mw=11,711 withpolydispersity 1.67.

Example 5

[0063] The following example illustrates the use of the method of thisinvention on the purification of a copolymer of4-acetoxystyrene/tert.-butyl acrylate. 3282.8 g 4-acetoxystyrene, and254 g tert-butyl acrylate is polymerized in 3140 g methanol using 204.3g tert-butyl peroxypivalate as a catalyst. A sample of the polymer isisolated for analytical purposes. After polymerization was complete,1390 g of methanol was removed at 58° C. and replaced with 1392 g offresh methanol. The slurry was heated to reflux and cooled to 48° C.Another 1595 g of methanol was removed and replaced with 1590 g of freshmethanol. Again the slurry was heated to reflux and cooled. The methanolwas removed and replaced with 1800 g of fresh methanol and the mixturewas then transesterified with 39.8 g sodium methoxide. Thepolydispersity value of the purified polymer is 12% lower than the valueof the crude polymer.

[0064] While specific reaction conditions, reactants, and equipment aredescribed above to enable one skilled in the art to practice theinvention, one skilled in the art will be able to make modifications andadjustments which are obvious extensions of the present inventions. Suchobvious extensions of or equivalents to the present invention areintended to be within the scope of the present invention, asdemonstrated by the claims which follow.

What is claimed is:
 1. (Twice amended) A method of purifying crudepolymers derived from acyloxystyrene of the group consisting of

wherein R is either —OC(O) R⁵ or —OR⁵; as a homopolymer and/or with oneor more of the following monomers: an acrylate monomer having theformula II,

and/or with one or more ethylenically unsaturated copolymerizablemonomers taken from the group consisting of styrene, 4-methylstyrenestyrene alkoxide wherein the alkyl portion is C₁-C₅ straight or branchchain, tert.-butylstyrene, cyclohexyl acrylate, tert.-butyl acrylate,tert.-butyl methacrylate, maleic anhydride, dialkyl maleate, dialkylfumarate and vinyl chloride, wherein: i) R¹ and R² are the same ordifferent and independently selected from the group consisting of:hydrogen, fluorine, chlorine. bromine, alkyl and fluoroalkyl grouphaving the formula C_(n)H_(x)F_(y) where n is an integer from 1 to 4, xand y are integers from 0 to 2n+1, and the sum of x and y is 2n+1,phenyl, and tolyl; ii) R³ is selected from the group consisting of:hydrogen, methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, andtert.-butyl; iii) R⁴ is methyl, ethyl, n-propyl, iso-propyl andtert.-butyl; and iv) R⁵ is C₁-C₄ alkyl consisting essentially ofsubjecting said crude polymer, after polymerization thereof, to afractionalization procedure wherein said crude polymer in an alcoholicsolvent is (a) suspended therein and with additional solvent is added,(b) heated and/or stirred for a sufficient period of time to permitdissolution of the undesirable materials in said crude polymer, (c)cooling the resultant mixture, (d) separating the alcoholic solvent fromsaid polymer and (e) repeating said steps (a)-(d) until thepolydispersity value of the purified polymer is about 10% less than thatpolydispersity value of the crude polymer.
 2. The process as set forthin claim 1 wherein the solvent is selected from the group consisting ofmethanol, ethanol, propanol, isopropanol, t-butanol and mixturesthereof.
 3. The process as set forth in claim 1 wherein theacyloxystyrene is acetoxystyrene monomer and is the only monomer used.4. The process as set forth in claim 3 wherein the p-acetoxystyrenepolymer in purified form has a polydispersity value of less than about2.0.
 5. The process as set forth in claim 4 wherein the solvent ismethanol.
 6. The process as set forth in claim 1 wherein there is anadditional step of transesterification of the purified polymer in thealcoholic solvent in the presence of catalytic amounts of a catalyst. 7.The process as set forth in claim 6 wherein after thetransesterification step, there is an additional step of removing thecatalyst from the reaction mixture of the transesterified product bypassing said product through an ion-exchange bed in order to remove saidcatalyst therefrom.
 8. The process as set forth in claim 7 wherein theentire process is conducted on an anhydrous basis.
 9. The process as setforth in claim 8 wherein in step (e) the fractionalization is conductedfrom about 2 to about 10 times.
 10. The process as set forth in claim 9wherein after the catalyst removal step, there is an additional stepwherein said alcoholic solvent is removed and replaced by a photoresistcompatible solvent.